INVESTIGATIVE REPORTING: Give Clark a power action. Choose an opposing character within 6 squares. That character can't use Stealth this turn and their combat values cannot be modified this turn.
Can this stop a character from using the Gauntlet for a turn?

It would keep the Gauntlet user from using the modifiers gained on special powers 2 and 3, but they'd still be able to use any gems or powers gained (except Stealth, of course).

If by "using" you mean "having their combat values modified by", then yes.

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My answer is yes, Investigative Reporting will negate Stealth and combat value mods from the IG.

Agreed. Filler.